Rolling mills



United States Patent OfiFice US. Cl. 72-244 9 Claims ABSTRACT OF THE DISCLOSURE The disclosure of the present invention relates to a rolling mill having a pair of spaced housings for rotatably supporting a pair of roll assemblies. The top roll assembly is adjusted by power driven wedges arranged between the housings and the roll assembly to place the housings under a stretched condition by forcing the roll assemblies together. Between the top roll assembly and the housings struts are located which after the housings are placed in the stretched condition are brought into engagement with the housings and the top roll assembly, so that the struts hold the housings in the stretched condition leaving the top roll assembly free to be adjusted to set the roll gap of the mill.

This invention relates to a rolling mill method, apparatus, and control system and is particularly concerned with rolling mill stands which are prestressed. In other words, the stand housings are subject to a stress applied prior to rolling and subsisting during rolling.

There have been numerous proposals for prestressed stands in the past, because such stands have the advantage of high stiffness, which results in a relative diminution of gauge errors in the material being rolled, particularly where there is no automatic gauge control system provided for the stand. Usually, the stand is prestressed by hydraulic means, these means being in addition to some mechanism for setting the roll gap. The provision of the hydraulic prestressing means in addition to the setting means has caused complication and added expense of the stand.

In accordance with the present method, apparatus, and control system of the present invention, a rolling mill stand comprises housings, each if which supports bearing chocks for the rolls, mechanical struts for holding the housings in tensioned condition and means for adjusting the roll gap. Preferably, the roll gap adjusting means are used to tension the housings initially, the mechanical struts thereafter maintaining the tensioned condition. In this way, the use of two separate control mechanisms is avoided. The roll gap adjusting means can be any of the devices known for such a duty such as screws, wedges or hydraulic cylinders.

The invention will be more readily understood by way of example from the following description of a rolling mill stand in accordance therewith, reference being made to the accompanying drawings in which:

FIGURE 1 shows in diagrammatic form an end view of the stand in the direction of the roll axis, and the associated control mechanism,

FIGURE 2 shows a wedge unit.

The stand has a pair of simple, closed loop, housings, one of which is shown in FIGURE 1 at 12, it being understood that the other housing is behind housing 12 and is spaced from it in the direction of the axis of the rolls. Each housing 12 has a housing window 13 in which is located the bearing chock 14 for the lower back-up roll 15. Chock 14 rests on a packer 16 while its upper surface is engaged by a pair of compression bars 17 located 3,507,139 Patented Apr. 21, 1970 one on each side of the window 13. Packer 16 is adjustable in size and is used to accommodate large variations in roll size.

The chock 18 for the upper back-up roll 20 slides vertically within the housing window and contains the bars 17 and is separated from the top of the housing window 13 by a wedge unit 21 and a load cell 22. The chocks 23 for the work rolls 24 are nested in recesses in the back-up rolls 14, 1-8.

As shown in FIGURE 2, each of the wedge units 21 is constituted by a first wedge member 25 secured to the housing 12 at the top of the window 13 and having a tapered lower surface, and a moving wedge member 26, which has a correspondingly tapered upper surface engaging the lower surface of member 25. The moving wedge member 26 is attached by a rod 27 to a piston and cylinder assembly (not shown) to cause horizontal movement of member 26 and thereby to adjust the separation of the top of the chock 18 from the top of the housing 12. This is the embodiment shown but it will be appreciated that the wedge can be actuated by any well known device which has a nut and screw which can be driven from a rotary motor or electric motor. To enable the wedge unit to operate under the rolling load encountered during rolling, the surfaces of the moving wedge member 26 are preferably provided with anti-friction material; this may be done by applying to those surfaces permanent layers of polytetrafluorethylene, or by supplying oil under pressure to the surfaces, so that they are separated by the corresponding surfaces of membe 25 and load cell 18 by a layer of oil under pressure. Again, the wedge member 26 may have on its bearing surfaces roller bearings.

Reverting to FIGURE 1, each of the compression bars 17 is provided with a wedge unit 31 and a packer 32. The 'wedge unit 31 may be similar to the unit shown in FIGURE 2, but as unit 31 is not normally required to be operated under load, the special anti-friction means may be dispensed with.

In operation, the wedge units 21 are first operated, with no material between the work rolls 24, in order to apply a tension to housings 12 in excess of the maximum rolling load likely to be encountered in practice. This loading of the mill could take place through the rolls or by the interposition of packers between the back-up chooks. With the housings in tension and thus stretched vertically, the packer 32 and wedge unit 31 of each compression bar 17 is placed in position and the wedge unit 31 adjusted to take up any clearance between the top of the packer 32 and the housing top. Then, wedge units 21 are returned to their original positions, so opening the roll gap, the housings 12 being held in the tensioned condition by the mechanical struts constituted by the compression bars 17, wedge units 31 and packers 32. If packers were interposed between the back-up chocks, they are now removed. The roll gap is adjusted to the required value for rolling, by operation of the wedge units 21 and rolling commenced. During the rolling operation, the wedge units 21 can be adjusted for gauge control, either by hand or by an automatic control system as indicated in FIGURE 1.

Because the prestressing of the mill structure in the manner described shortens the stress path set up in the mill structure by the rolling load, the stand is very stiflf and material rolled by it is more uniform in thickness than in conventional, uncompressed stands. Furthermore, the stand is stiffer than a similar mill preloaded by hydraulic means because the compliance of the hydraulic medium significantly affects the overall mill stifiness.

If the uniformity of thickness of the rolled material is required to be improved still further, a automatic control system as illustrated in FIGURE 1 may be employed. The

roll gap, which is equal to the thickness of the rolled material, is

S -l-F/M where S is the separation of the work rolls 24 for zero rolling load with the housings pretensioned,

F is the rolling load,

M is a spring co-efiicient dependent on the stiffness of the mechanical struts Hand 32, the housings and the rolls.

If h is the required thickness of the strip, any departure signal 6 of the material from the required value is given by This departure may be used to control the wedge units 21 in tandem to maintain the departure substantially zero, i.e. the thickness of the rolled material at the required value h.

In FIGURE 1, the wedge units 21 are shown as controlled in tandem by a control mechanism 33, which controls the positioning of the wedge members 26 by the departure signal 6 on line 34. The piston and cylinder assemblies for the two units 21 are cross-connected so that the positions of the members 26 in two units correspond at all times. The mechanism 33 gives at line 35 a signal representing the positions of the wedge members 26; this signal represents S The signals from the two load cells 22 are summed and appear on line 37, to represent F/The desired thickness h is derived from a manually set potentiometer 38, the h signal appearing on line 39. The signals on lines 35, 37 and 39 are applied to a computing circuit 40 which solves the equation and gives the departure signal on the output line 34 controlling themechanism 33.

As will be appreciated, any change in the rolling load F, due to changes in the characteristics of the material entering the stand, results in the production of a departure signal :5 to alter the position of the wedge units 21, and thus the rollgap, until the departure signal is again returned to zero when the stand will roll the required thickness material.

We claim:

1. A rolling mill stand comprising a pair of spaced housings, each having a housing window, and, for each said housing, a first roll bearing chock non-adjustably located at one end of said window, a second roll bearing chock adjustably mounted in said window, means for adjusting said second chock in the said window to vary the roll gap, and at least one mechanical strut functionally engaging said housing at its ends and so arranged and dimensioned that said strut holds said housing in a stretched condition and is held in compression by virtue only of the stretched housing.

2. A rolling mill stand according to claim 1 in which the adjusting means are arranged to tension the housings, the struts thereafter maintaining the housings in tensioned condition.

3. A rolling mill stand according to claim 1 in which the roll gap adjusting means are wedges.

4. A rolling mill stand comprisinga pair of spaced housings, each having a housing window, and, for each said housing, a first roll bearing chock non-adjustably located at one end of said window, a second roll bearing chock adjustably mounted-in said window, means for adjusting said second chock in said window to vary the roll gap, and at least one mechanical strut, one end of which engages said first chock and the other end of which engages the end of said window remote from said first chock, said strut having an unstressed length greater than the separation of said first chock and said remote end when the housing is unstressed, whereby said strut holds said housing in a stretched condition.

5. A rolling mill stand according to claim 4 in which the adjusting means comprise a Wedge unit for each housing.

6. A four-high rolling mill stand according to claim 4 in which the checks mounted in the housings are the back-up roll chocks.

7. In a method of operating a rolling mill and like device having a windowed housing and a first roll hearing chock non-adjustably located at one end of said housing window, a second roll bearing chock located in said window, and means for adjusting said second roll bearing chock towards and away from said first bearing chock, the steps of applying a prestress force to said housing to place the housing in a stretched condition, functionally engaging said housing when in said stretched condition with a strut arranged in said window in a manner that said strut is held in compression by virtue only of the stretched housing.

8. In a method of operating a rolling mill and like device having a windowed housing and a first roll bearing chock non-adjustably located at one end of said housing window, a second roll bearing chock located in said window, and means for adjusting said second roll bearing chock towards and away from said first bearing chock, the steps of advancing said second roll bearing chock towards said first roll bearing chock in a manner to place the housing in a stretched condition, functionally engaging said housing when in said stretched condition with a strut arranged in said window, retracting said second roll bearing chock to place the strut in compression by virtue only of the stretched condition of the housing, and, after said strut is held in compression by said housing, adjusting said second roll bearing chock towards and away from said first roll bearing chock to vary the roll gap.

9. A rolling mill stand comprising a pair of spaced housings, each having a housing window, a first roll hearing chock non-adjustably located at one end of each window for rotatably supporting a first roll, a second roll hearing chock adjustably mounted in each window for rotatably supporting a second roll, means for adjusting the second chocks in said windows relative to the first chocks, means for operating the adjusting means to place said second roll in a first position to subject the housings in the direction of the separating force of the rolls to a stretch condition, a mechanical strut for each housing functionally engaging said housings at their ends and so arranged and dimensioned that said struts hold said housings in a stretched condition and are held in compression by virtue only of the stretched housings, and means for operating said adjusting means to place said second roll in a second position to set the roll gap of the mill.

References Cited UNITED STATES PATENTS 3,124,982 3/1964 Newmann 7221 3,217,525 11/1965 Howard 72237 3,247,697 4/1966 Cozzo 72-240 3,286,501 11/1966 Tracey 72237 3,327,508 6/ 1967 Brown 726 3,362,204 1/1968 Scott 72245 3,368,381 2/1968 Frohling et al 72245 3,369,383 2/1968 Barnikel 72245 MILTON S. MEHR, Primary Examiner US. Cl. X.R. 728= 

